U.S. patent number 3,980,813 [Application Number 05/531,050] was granted by the patent office on 1976-09-14 for aperture correction circuit.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Kinya Shinkai.
United States Patent |
3,980,813 |
Shinkai |
September 14, 1976 |
Aperture correction circuit
Abstract
An aperture correction circuit is disclosed in which the first
portions of the differentiated signals of input video signals are
inverted, and the waveform shaped signals thus obtained and the
input video signals are added together whereby the corrected video
signals having sharp edged waveforms are obtained.
Inventors: |
Shinkai; Kinya (Yokohama,
JA) |
Assignee: |
Sony Corporation (Tokyo,
JA)
|
Family
ID: |
15296827 |
Appl.
No.: |
05/531,050 |
Filed: |
December 9, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Dec 17, 1973 [JA] |
|
|
48-141644 |
|
Current U.S.
Class: |
348/625;
348/E5.076 |
Current CPC
Class: |
H04N
5/208 (20130101) |
Current International
Class: |
H04N
5/208 (20060101); H04N 005/14 () |
Field of
Search: |
;178/7.1R,7.3R,7.5R,DIG.25,DIG.34,7.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Martin; John C.
Attorney, Agent or Firm: Eslinger; Lewis H. Sinderbrand;
Alvin
Claims
I claim as my invention:
1. An aperture correction circuit comprising:
A. a differentiating circuit for differentiating an input
signal;
B. polarity determining means for separating the differentiated
signal into corresponding first and second signals of opposed
respective polarities said first signal consisting of:
1. those portions of said differentiated signal produced when the
differential of said input signal is positive and inverted
reproductions of those portions of said differentiated signal
produced when the differential of said input signal is negative,
and
2. said second signal consisting of those portions of said
differentiated signal produced when the differential of said input
signal is negative and inverted reproductions of those portions of
said differentiated signal produced when the differential of said
input signal is positive;
C. switching means operative to alternately conduct selected
intervals of said first and second signals;
D. switch control means responsive to said differentiated signal to
control said switching means so that the ouput signal of the latter
corresponds to said second signal during those intervals when the
second differential of said input signal is positive and
corresponds to said first signal during those intervals when the
second differential of said input signal is negative; and
E. an adding circuit which adds said output signal of the switching
means to said input signal for obtaining an aperture corrected
signal from said adding circuit.
2. An aperture correction circuit according to claim 1, wherein
said switching means comprises first and second rectifying bridge
means alternately rendered conductive by said switch control
means.
3. An aperture correction circuit according to claim 1, wherein
said polarity determining means comprises a phase splitter
receiving said differentiated signal and yielding signals which are
respectively in phase with said differentiated signal and
180.degree. out of phase in respect to the latter, and means having
first and second output terminals for conducting oppositely
polarized portions of said signals yielded by the phase splitter to
said first and second output terminals, respectively, to there
provide said first and second signals of opposed respective
polarities.
4. An aperture correction circuit according to claim 3, wherein
said means for conducting oppositely polarized portions of said
signals yielded by the phase splitter to said first and second
output terminals comprises a bridge rectifier having said first and
second output terminals at opposed locations, and first and second
input terminals at opposed locations on said bridge rectifier and
respectively receiving said signals which are in phase with said
differentiated signal and 180.degree. out of phase in respect to
the latter, so that during such periods that a signal received at
either of said input terminals is of a first polarity, it is
conducted to said first output terminal, and during such periods
that a signal received at either of said input terminals is of a
second polarity, it is conducted to said second output
terminal.
5. An aperture correction circuit according to claim 1, wherein
said switch control means comprises an additional differentiating
circuit for yielding a twice differentiated signal, a limiter for
limiting said twice differentiated signal and a phase splitter
receiving the limited twice differentiated signal and yielding
first and second control signals which are respectively in phase,
and 180.degree. out of phase in respect to the limited twice
differentiated signal for application to said switching means so as
to render the latter operative to alternately conduct said signals
of first and second opposed polarities.
6. An aperture correction circuit according to claim 5, wherein
said switching means comprise first and second rectifying bridge
means, each of said rectifying bridge means having an input
terminal, an output terminal opposite said input terminal, and
first and second control terminals at opposed locations on said
rectifying bridge means, said input terminals respectively
receiving said first and second signals of opposed respective
polarities, said first control signal being applied to the first
control terminal of each of said rectifying bridge means, said
second control signal being applied to the second control terminal
of each of said rectifying bridge means, so that when said first
control signal is in a first opposed polarity with respect to said
second control signal, the first rectifying bridge means conducts
said first signal of opposed respective polarity to its output
terminal for application to said adding circuit, and when said
first control signal is in a second opposed polarity with respect
to said second control signal, the second rectifying bridge means
conducts said second signal of opposed respective polarity to its
output terminal for application to said adding circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an aperture correction circuit,
and more particularly to an aperture correction circuit by which
ideal corrected video signals having sharp edged waveforms are
obtained.
2. Description of the Prior Art
In television receivers or the like, the sharpness of a reproduced
picture is limited by the frequency and phase response of the video
channels of the receivers and by the size of the beam spot on its
cathode ray tube.
In order to improve the picture sharpness, so-called aperture
correction circuits are provided which are well known in the prior
art.
Conventional aperture correction circuits of the prior art perform
their operations by superimposing twice-differentiated signals of
input video signals on the input video signals.
However, in actual television receivers and the like, the input
video signals have relatively dull edged waveforms so that
correcting signals having sharp waveforms can't be obtained just by
differentiating the input video signals. That is, the input video
signals can't be corrected sufficiently.
OBJECT OF THE INVENTION
Accordingly, it is an object of this invention to provide a novel
aperture correction circuit avoiding the above-mentioned
disadvantages inherent in the prior art.
It is another object of this invention to provide an improved
aperture correction circuit for television receivers and the
like.
It is a further object of this invention to provide a novel
aperture correction circuit which can correct input video signals
ideally even when the input signals have relatively dull edged
waveforms.
SUMMARY OF THE INVENTION
The present invention provides a novel aperture correction circuit
which can sharpen the edge portions of input video signals
sufficiently. The aperture correction circuit according to this
invention includes a differentiating circuit, a waveform shaping
circuit and an adding circuit.
The input video signals, which are supplied to the aperture
correction circuit from an appropriate video signal source, are
supplied to the differentiating circuit and the adding circuit
simultaneously.
The differentiated signals from the differentiating circuit are
supplied to the waveform shaping circuit and first half portions of
the differentiated signals are inverted by the waveform shaping
circuit. The waveform shaped signals from the waveform shaping
circuit are supplied to the adding circuit whereby aperture
corrected signals are derived from the adding circuit.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1A to FIG. 1D, inclusive, show waveform diagrams used for
explaining the principle of this invention;
FIG. 2 shows a circuit diagram illustrating an embodiment of the
aperture correction circuit according to the present invention;
and
FIG. 3A to FIG. 3I, inclusive, show waveform diagrams used for
explaining the operation of the circuit shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1A to FIG. 1D show waveform diagrams which are used for
explaining the principle of an embodiment of this invention. FIG.
1A shows a leading edge of an input video signal S.sub.1 and FIG.
1B shows a differentiated signal S.sub.2 of the input signal
S.sub.1. By inverting a first half portion (illustrated by
hatching) of the differentiated signal S.sub.2, a correcting signal
S.sub.3 is obtained, as shown in FIG. 1C. And ideally corrected
video signal S.sub.4 having a sharp leading edge is obtained by
superimposing the correcting signal S.sub.3 on the input video
signal S.sub.1, as shown in FIG. 1D.
An embodiment of the aperture correction circuit according to the
invention based upon the above principle will be now described with
reference to FIGS. 2 and 3. In FIG. 2, reference numeral 1
indicates an input terminal to which an input signal S.sub.5 having
dull edges, as shown in FIG. 3A, is applied. A corrected signal
which consists of the input signal S.sub.5 and a correcting signal
superimposed on the former is delivered to an output terminal 2. In
this case, the input signal S.sub.5 is supplied to a first
differentiating circuit consisting of a capacitor 3 and a resistor
4 to be differentiated and then supplied to the base of a
transistor 5 to be phase-inverted. Thus, the signal appearing at
the collector of the transistor 5 or at a point B is a
once-differentiated signal S.sub.6 which is phase-inversed as shown
in FIG. 3B. The once-differentiated signal S.sub.6 is applied to
the base of a transistor 6 for phase-splitting. An output signal
obtained at the emitter of the transistor 6 is supplied to a second
differentiating circuit consisting of a capacitor 7 and a resistor
8 to be differentiated thereby. Thus, an output signal appearing at
the ouput terminal of the second differentiating circuit or at a
point C is a twice-differentiated signal S.sub.7 as shown in FIG.
3C. The ouput signal S.sub.7 from the second differentiating
circuit is applied to the base of a transistor 9 with an emitter
grounded to be phase-inverted and thereafter is applied to a
limiter 10 consisting of two diodes connected in parallel with
opposite polarities. Accordingly, a pulse signal S.sub.8, as shown
in FIG. 3D, is obtained at the output terminal of the limiter 10 or
at a point D. The pulse signal S.sub.8 shown in FIG. 3D is then
supplied to the base of a transistor 11 for phase-splitting, so
that a switching signal S.sub.8 in phase with the pulse signal
S.sub.8 is obtained at the emitter of the transistor 11 or at a
point D' while a switching signal S.sub.9 in reverse phase with the
switching signal S.sub.8, as shown in FIG. 3E, is obtained at the
collector of the transistor 11 or at a point E. These switching
signals S.sub. 8 and S.sub.9 are supplied to bridge-connected diode
switching circuits 12A and 12B, respectively. Generally speaking,
the circuit elements 7 through 11 comprise an embodiment of a
switch control means responsive to the once-differentiated signal
S.sub.6 and controlling a switching means, such as bridge
rectifiers 12A and 12B, so that the output of the latter
corresponds to the differentiated signal with the first half
portion of the latter being inverted.
It is assumed that a point of the switching circuit 12A supplied
with the switching signal S.sub.8 is taken as a first control
terminal, a.sub.1 and a point thereof supplied with the switching
signal S.sub.9 is taken as a second control terminal, b.sub.1. In
the switching circuit 12A a series connection of diodes D.sub.1 and
D.sub.2 and another series connection of diodes D.sub.3 and
D.sub.4, whose forward directions are selected from the point
a.sub.1 to the point b.sub.1, are connected in parallel. In this
case, the connection point between the diodes D.sub.1 and D.sub.2
is made as an input terminal c.sub.1 and the connection point
between the diodes D.sub.3 and D.sub.4 is made as an ouput terminal
d.sub.1. In this switching circuit 12A, resistors are connected in
parallel to the diodes D.sub.1 to D.sub.4, respectively. Similarly,
the other switching circuit 12B is formed of diodes D.sub.5 to
D.sub.8 connected in bridge and resistors connected in parallel
thereto, respectively. In the switching circuit 12B, a series
connection of the diodes D.sub.6 and D.sub.5 and another series
connection of the diodes D.sub.7 and D.sub.8, which is connected in
parallel to the former, are connected in forward direction from a
second control terminal, b.sub.2, supplied with the switching
signal S.sub.9 to a first control terminal, a.sub.2, supplied with
the switching signal S.sub.8. The resistors respectively connected
in parallel to the diodes D.sub.1 to D.sub.4 of the switching
circuit 12A and the resistors respectively connected in parallel to
the diodes D.sub.5 to D.sub.8 of the switching circuit 12B are
selected relatively high in resistance to make their output voltage
zero when each of the diodes is non-conductive.
The input terminal c.sub.1 of the switching circuit 12A is supplied
with a signal S.sub.10 shown in FIG. 3F which is produced by
arranging the once-differentiated signal S.sub.6 shown in FIG. 3B
in negative polarity, while the input terminal c.sub.2 of the
switching circuit 12B is supplied with a signal S.sub.11 shown in
FIG. 3G which is produced by arranging the once-differentiated
signal S.sub.6 shown in FIG. 3B in positive polarity. This function
of generating signals s.sub.10 and S.sub.11 is accomplished by
circuits provided with the once-differentiated signal S.sub.6 and
described generally as polarity determining means. Thus, the
negative portion of the once-differentiated signal appearing at the
collector of the transistor 6 (which is in reverse phase with the
signal S.sub.6 shown in FIG. 3B) and the negative portion of the
once-differentiated signal appearing at the emitter of the
transistor 6 (which is in phase with the signal S.sub.6 shown in
FIG. 3B) are transmitted through diodes 13A and 14A to a point F as
a signal S.sub.10 shown in FIG. 3F. At the same time, the positive
portion of the once-differentiated signal appearing at the
collector of the transistor 6 and the positive portion of the
once-differentiated signal appearing at the emitter of the
transistor 6 are transmitted through diodes 13B and 14B to a point
G as a signal S.sub.11 shown in FIG. 3G so that first and second
signals of opposed respective polarities irrespective of the
polarity of the differentiated signal S.sub.6 are provided at
points F and G. Note that diodes 13A, 14A, 13B and 14B together are
arranged as a bridge rectifier. The ouput terminals d.sub.1 and
d.sub.2 of the switching circuits 12A and 12B are connected
together through resistors, and then a composite output signal of
the switching circuits 12A and 12B is delivered through a capacitor
to a point H as a composite signal S.sub.12 as shown in FIG. 3H.
The composite output signal S.sub.12 delivered to the point H is
added through a variable resistor 15 to the input terminal 1.
With the illustrated and described embodiment of the invention, in
the time period when the switching signal S.sub.8 is positive but
the switching signal S.sub.9 is negative, the diodes D.sub.1 to
D.sub.4 of the switching circuit 12A are made conductive but the
diodes D.sub.5 to D.sub.8 of the switching circuit 12B are made
non-conductive. As a result, in this time period the former half of
the signals S.sub.10 is transmitted to the point H. While in the
time period when the switching signal S.sub.8 is negative but the
switching signal S.sub.9 is positive, the diodes D.sub.1 to D.sub.4
are made non-conductive but the diodes D.sub.5 to D.sub.8 are made
conductive with the result that the latter half portion of the
signal S.sub.11 is transmitted to the point H. When the switching
signals S.sub.8 and S.sub.9 are both zero, the diodes D.sub.1 to
D.sub.4 and the diodes D.sub.5 to D.sub.6 are made non-conductive
and hence the level at the point H is also zero.
Next, when the switching signal S.sub.8 becomes negative and the
switching signal S.sub.9 becomes positive, the diodes D.sub.1 to
D.sub.4 become non-conductive and the diodes D.sub.5 to D.sub.8
become conductive. When the polarities of the switching signals
S.sub.8 and S.sub.9 are reversed, the diodes D.sub.1 to D.sub.4
become conductive but the diodes D.sub.5 to D.sub.8 become
non-conductive. Consequently, switching means 12A and 12B operate
to alternately conduct the signals of first and second opposed
polarities provided by the polarity determining means and, as a
result, the correcting signal S.sub.12 shown in FIG. 3H
corresponding to the differentiated signal with the first half
portion of the latter being inverted is obtained at the point H.
This signal is added to the input signal S.sub.5 shown in FIG. 3A
from the input terminal 1. Therefore, at the output terminal 2
there is obtained an ideal rectangular shaped signal S.sub.13 which
has a substantially vertical rising up portion and sharp edges, as
shown in FIG. 3I.
Generally, speaking, the above described polarity determining
means, switching means and switch control means respond to the
differentiated input signal and cooperate to provide at the output
of the switching means a correcting signal S.sub.3 as illustrated
in FIG. 1C. Collectively, these three elements correspond to the
waveform shaping circuit.
As may be obvious from the above description, according to the
present invention, a video signal, whose rising up portion is not
vertical but inclined from the vertical and whose edges are dull,
can be made to be an ideal one whose rising up portion is
substantially vertical and whose edges are sharpened.
Accordingly, if the present invention is inserted into, for
example, the luminance signal and chrominance signal sytems, the
sharpness of a picture and the contour of its color can be made
clear.
The foregoing description is given for only one preferred
embodiment of the present invention, but it may be apparent that
many modifications and variations could be effected by one skilled
in the art without departing from the spirits or scope of the novel
concepts of the present invention.
* * * * *